Composite material and use thereof for controlling thermal effects in a physicochemical process

ABSTRACT

The invention relates to a composite material, a method for controlling the thermal effects generated in a physicochemical process using said material, and applications of the material and the method. The composite material comprises an active solid and a phase change material. The phase change material takes the form of micronodules having an average size of between 1 micron and 5 millimeters and it is selected from materials with a liquid/solid phase change temperature of between −150° C. and 900° C. The active solid is selected from solids that can be used in a method involving reversible physicochemical processes that are exothermic in one direction and endothermic in the opposite direction.

The present invention relates to a composite material, a method forcontrolling the thermal effects generated in a physicochemical processusing said material, and applications of the material and the method.

In various technical fields, the methods put into practice are based ona reversible physicochemical process that is exothermic in one directionand endothermic in the other. In this type of method, it is generallydesirable to remove the heat liberated during the exothermic step, andit is necessary to supply the heat necessary for the endothermic step toobtain satisfactory results.

The storage of a gas in an adsorbent solid is widely investigated andemployed. The adsorption of the gas on the solid is exothermic and theheat liberated has a detrimental effect on adsorption efficiency.Moreover, a reverse problem arises during the desorption of the gasduring the regeneration step. In fact, this desorption generates anendothermic effect that is even greater when the regeneration step iscarried out at high gas flow rates. This endothermic effect stronglyinhibits the desorption of the gas, and the kinetics of the method areaccordingly limited by the heat input necessary. The usual solutionsconsist, in the case of adsorption for example, in removing the heatformed to the exterior, necessitating the use of a very high thermalconductivity material as adsorbent solid. This high thermal conductivitycan be obtained by adding expanded natural graphite (ENG) to activatedcharcoal [S. Biloé, et al., Carbon, 2001, 39(11), 1653-1662)] or byusing an ENG-activated charcoal composite prepared by in situ activation(WO01/55054).

The storage of energy on composite materials containing a phase changecomponent has also been investigated. These materials neverthelesspresent very poor thermal conductivities (about 0.2 W·K⁻¹m⁻¹). Inactivated charcoal-paraffin composites in which the activated charcoalis impregnated with paraffin, the confinement of the paraffin in themicropores of the activated charcoal inhibits the energy properties ofphase change inherent in the paraffin [C. Chapotard, et al., (Entropie1982; 107-108: 112-121)]. Composite materials comprising expandednatural graphite (ENG) and paraffin have also been described (X. Py, etal, International Journal of Heat and Mass Transfer, 2001, 44,2727-2737). ENG is impregnated with the paraffin by simple capillarity.The thermal conductivity of this composite corresponds to that of ENG,which then only serves as container and thermal conductor. Thiscomposite material does not contain activated charcoal and hence doesnot display any adsorption capacity. Sweating of the paraffin is alsoobserved during the use of this type of composite.

Patent WO98/04644 teaches a method and a system for storing heat or coldin a composite material comprising an expanded and compressed graphitematrix and a phase change material that can be, in particular, acongruent melting salt. The composite material is obtained by vacuumimpregnation of the matrix by a salt solution or by immersion of thematrix in a salt solution. As in the previous case, the objective ofthis type of material is exclusively to store energy in the form oflatent heat, and not to control the thermicity of a physicochemicalprocess combining a gas with an active solid. Also observed is thepresence of blooming problems of the phase change material, as in thecase of paraffin.

It is well known how to prepare micronodules of various materials. Forexample, the encapsulation of an odorant (Migrin Oil) is described by K.Hong et al. [Materials Chemistry and Physics, 58 (1999) 128-131]. Theencapsulation method consists in contacting a precondensate of melamineand formaldehyde in alkaline medium with an aqueous emulsion of MigrinOil and 1,4-diaminoanthraquinone (DDA). Furthermore, micronodules ofparaffin in a polymer envelope obtained by crosslinking a melamine resinare marketed by BASF AG. [E. Jahns, BASF, “Microencapsulated PhaseChange Material”,www.ket.kht.se/Avdelningar/ts/annex10/WS_pres/Jahns.pdf]

Composite materials are used in the textile field, comprising fibers ofmaterials conventionally used for textile fibers and micronodules of aphase change material. The micronodules can be grafted onto the fibersor distributed in the mass of material constituting the fibers. [G.Nelson, International Journal of Pharmaceutics. 2002, 242, pp. 55-62].

The problem that the invention proposes to solve is to remedy theinhibiting effect engendered by the heat liberated during the exothermicstep and by the heat consumed in the endothermic step in methodsinvolving a reversible physicochemical process that is exothermic in onedirection and endothermic in the opposite direction, and which takesplace in a solid material. The purpose is to control in situ the thermaleffects occurring during the physicochemical process, in order to ensureisothermal operation.

This is why the subject of the present invention is a composite materialcomprising an active solid and micronodules, a method for controllingthe thermal effects in a method involving a reversible physicochemicalprocess, and various applications of the material.

The composite material according to the invention comprises an activesolid and a phase change material and is characterized in that:

the phase change material takes the form of micronodules having anaverage size of between 1 micron and 5 millimeters;

the phase change material is selected from materials with a liquid/solidphase change temperature of between −150° C. and 900° C.;

the active solid is selected from solids that can be used in a methodinvolving reversible physicochemical processes that are exothermic inone direction and endothermic in the opposite direction.

The range of reversible physicochemical processes include the following:

reversible chemical reactions that are exothermic in the synthesisdirection and endothermic in the decomposition direction;

reversible mechanisms of exothermic adsorption and endothermicdesorption of a gas on a solid.

In a composite material according to the invention, the active solid maytake the form of particles or monoliths. A monolith consists of aconsolidated assembly of several particles and it displays macroscopiccohesion.

Materials that can be used as active solid in a reversible chemicalreaction are reactive solids. Examples include various salts such ashalides, carbonates and hydroxides. In particular, chlorides such as,for example, BaCl₂, LiCl, CaCl₂, MnCl₂, NiCl₂ or bromides such as, forexample, SrBr₂ react with ammonia or with water; hydroxides such asSr(OH)₂ or Ba(OH)₂ react with water; carbonates react with carbondioxide.

Materials that can be used as active solid in a reversible adsorptionare porous and/or microporous solids. Examples include activatedcharcoals, zeolites, activated alumina and silica gels.

The phase change material can be selected, for example, from paraffins,congruent melting salts and metals. A micronodule consists of said phasechange material encapsulated in an envelope of a material adapted to thepressure and temperature requirements of the method for which the use ofthe micronodules is considered, and compatible with the active solidwith which the micronodules are in contact.

Paraffins consist of pure alkanes or mixtures of alkanes with 1 to 100carbon atoms.

If the liquid/solid phase change material is a salt, it can be selectedin particular from hydrated or unhydrated halides such as for exampleCaBr₂, CaCl₂, KF, KCl, MgCl, NaCl, NaF, NH₄Cl, NH₄F, ZnCl₂.5H₂O,KF.4H₂O, CaCl.6H₂O, hydrated or unhydrated carbonates such as forexample LiClO₃.3H₂O, hydrated or unhydrated sulfates such as for exampleMgSO₄, ZnSO₄, Na₂SO₄, Na₂SO₄.10H₂O, (NH₄)₂SO₄, phosphates such as forexample Na₂HPO₄, NaH₂PO₄, NH₄H₂PO₄, nitrates such as for example NH₄NO₃,Al(NO₃)₃, Ca(NO₃)₂, Cd(NO₃)₂, KNO₃, LiNO₃, Mg(NO₃)₂, NaNO₃, Ni(NO₃)₂,Zn(NO₃)₂, Zn(NO₃)₂.6H₂O, Cu(NO₃)₂, and hydroxides such as for exampleBa(OH)₂, NaOH.

Examples of metals that can be used as phase change material include Al,Pb, Cu, Zn and alloys thereof.

Paraffins are a particularly advantageous family of materials becausethey cover a broad range of liquid/solid phase change temperatures.

Of course, the phase change material is selected as a function of theactive solid which is the seat of the reversible physicochemicalprocess, and of the desired phase change temperature.

The respective proportions of active solid and micronodules can beadjusted so that the heat flux generated by the physicochemical processused in the method is totally or partially stored or restored by theliquid/solid phase change.

Similarly, the size of the micronodules used can advantageously beadjusted to the thermal power generated by the physicochemical process.

The composite material according to the invention can be obtained invarious forms. In a first embodiment, the material comprises a porous ormicroporous active solid, in the form of monoliths or particles, themicronodules occupying the pores of the active solid. In a secondembodiment, the composite material is a simple mixture of particles ormonoliths of active solid and micronodules, the micronodules occupyingthe spaces between the particles or monoliths of active solid. In athird embodiment, the composite material comprises particles ormonoliths of active solid on the surface of which the micronodules arefixed, either by chemical grafting or by bonding with an adhesive. In afourth embodiment, the particles of active solid (smaller than themicronodules) are fixed on the surface of the micronodules by chemicalgrafting or by bonding with an adhesive. In a fifth embodiment, thematerial comprises a mixture of particles of a preferably highlyconducting material on which the micronodules are fixed, and particlesor monoliths of active solid. In a sixth embodiment, the compositematerial comprises one or more monoliths of active solid in which themicronodules are distributed.

The composite material may further contain expanded natural graphite. Itaccordingly takes the form of a matrix consisting of expanded graphiteand possibly a mechanical binder, within which the particles of activesolid and the micronodules of phase change material are distributed.

The materials proposed are advantageously used in all the methods inwhich a material is the seat of undesirable thermal effects. They serveto control the thermal effects locally by storing and by liberating theheat produced or demanded by the physicochemical process involved. Thusa method can operate in isothermal mode while it is the seat ofendothermic and exothermic mechanisms.

The method according to the invention for controlling thermal effects ina reversible physicochemical process between an active solid and agaseous compound, said process being exothermic in one direction andendothermic in the opposite direction, is characterized in that thethermal effects are controlled by using a composite material accordingto the invention as active solid.

The method for preparing the composite material according to theinvention depends on the type of active solid and of the micronodules ofwhich it is comprised, on the form in which it is to be used, and on thethermal effects which must be controlled and the dimensional constraintsassociated with the satisfactory operation of the method for which thecomposite material is intended.

A composite material according to the invention comprising a simplemixture of particles or monoliths of active solid and micronodules, inwhich the micronodules occupy the spaces between the particles or themonoliths of active solid, is obtained by mixing the preconstitutedmicronodules of phase change material and the particles or monoliths ofactive solid, in order to ensure satisfactory thermal contact.

A composite material according to the invention, comprising a mixture ofparticles of a preferably highly conducting material on which themicronodules are fixed, and particles or monoliths of active solid, canbe obtained by fixing the micronodules, for example by chemicalgrafting, on said support material and then mixing the grafted supportmaterial and the particles or monoliths of active solid in order toensure satisfactory thermal contact. Carbon fibers represent anadvantageous support material.

In a third embodiment, the micronodules, particles or monoliths ofactive solid, and a liquid adhesive, are mixed. The micronodules arethereby fixed on the particles or monoliths of active solid by bonding.If the size of the particles or monoliths of active solid is larger thanthat of the micronodules, a composite material is obtained comprisingparticles or monoliths of active solid on the surface of which themicronodules are fixed. If the size of the particles of active solid ismuch smaller than that of the micronodules, a composite material isobtained comprising micronodules on the surface of which the particlesof active solid are fixed.

It is thus possible to similarly obtain a material comprising particlesor monoliths of active solid coated with micronodules or a materialcomprising micronodules coated with particles of active solid, by usinga chemical reagent suitable for chemical grafting between the envelopeof the micronodules and the particles or monoliths of active solid.

A composite material comprising one or more monoliths of active solid inwhich the micronodules are distributed can be obtained by extrusion of apaste obtained by mixing the micronodules, the powdery active solid anda binder, followed by chemical or heat treatment to obtain the compositein solid form.

If the active solid is activated charcoal and the micronodules aremicronodules of paraffin, the composite material can be prepared bygrafting the micronodules onto the outer surface of the activatedcharcoal under the following conditions:

microencapsulated paraffin and activated charcoal are placed insuspension in a mixture of melamine and formaldehyde, at a pH of 8 and atemperature of 70° C.;

the pH is then lowered to 4, causing polymerization of the melamine andformaldehyde. Due to its hydrophobic character, the polymer forms a filmimprisoning the micronodules on the activated charcoal.

In a variant, the composite material comprising the micronodules and theactive solid is mixed with expanded natural graphite (ENG) and thecombination is compressed to obtain a block with high mechanicalstrength, good heat capacity and good thermal conductivity.

The use of a composite material according to the invention is suitablefor controlling the thermal effects at three levels during a methodusing a reversible physicochemical process, that is, the operatingtemperature level of the method is stabilized at the melting point ofthe phase change material used, the quantity of energy controlledcorresponds to the quantity of phase change material used, and the sizeof the micronodules is imposed by the thermal power that must becontrolled.

The materials proposed are advantageously used in methods in which areversible mechanism generates heat during an exothermic step andconsumes heat during an endothermic step, thereby respectivelyincreasing and decreasing the temperature of the active solid where themechanism occurs, thereby making it deviate from the operatingconditions that must be satisfied to obtain the optimal performance ofthe overall method.

The materials proposed in the present invention provide an advantageoussolution for maintaining the active solid at a substantially constanttemperature close to the melting point of the phase change materialused. Regardless of the method for preparing the composite, the use ofthe phase change material in the form of micronodules permits a rapidand uniform collection of the heat produced during the exothermic phase,said heat thus stored then being usable for the endothermic phase asrequired.

The composite materials according to the invention can advantageously beused as adsorbent beds in methods for purifying a gas mixture, accordingto the method called PSA (pressure swing adsorption), in which one ofthe gases is separated from the mixture by adsorption and regenerationby pressure modulation. Such a process consists in carrying out thesuccessive steps of pressurization and depressurization of an adsorbentbed by the gas mixture to be processed. The adsorption step,corresponding to pressurization, is exothermic. The desorption(regeneration) step, corresponding to depressurization, is endothermic.If the material of which the adsorbent bed is comprised is a compositematerial according to the invention, the heat produced in the exothermicstep is absorbed by the phase change material of the composite material,so that this step occurs at constant temperature. Then, the regenerationphase, which is endothermic and which corresponds to the desorption ofcertain components of the gas mixture, is carried out by using the heatrestored by the phase change material. This regeneraton step is hencealso isothermal. A further subject of the present invention isconsequently a method for purifying a gas mixture by adsorption andregeneration by pressure modulation, called the PSA method, consistingin carrying out the successive steps of pressurization anddepressurization of at least one adsorbent bed by a gas mixture, inorder to separate the gas mixture, said method being characterized inthat the adsorbent bed(s) comprise(s) a composite material according tothe invention.

The PSA method for the treatment of a gas mixture is particularly usefulfor obtaining hydrogen from a gas mixture, particularly from a gasmixture produced by methane reforming. This method is described inparticular by Warmuzinski K. and Tanczyk M., (Chem. Eng Pro. 1997;36:89-99). The average composition of the gas mixture issuing frommethane reforming is 70% H₂, 22% CO₂, 3% Co, 3% CH₄ and 2% N₂. The gasesare separated by means of two fixed adsorbent beds placed in series. Thebed of a first column traversed by the gas mixture to be processedcomprises an activated charcoal/micronodules composite materialaccording to the invention, the activated charcoal trapping CO₂ and CH₄during the adsorption phase. The bed of the second column comprises azeolite/micronodules composite material according to the invention, thezeolite adsorbing the traces of CO and nitrogen present in the mixture.The use of paraffin micronodules is particularly advantageous. At theoutlet of the columns, the H₂ content is at least 99.9%. The heatliberated by the steps of adsorption of CO₂ and CH₄ in the first column,and of CO and N₂ in the second column, is stored in the paraffinmicronodules in the form of latent heat of fusion, and is then used forthe desorption of the gases during the regeneration steps in thecolumns. Several sets of columns are used to obtain continuousproduction of H₂. A further subject of the present invention isconsequently a method for obtaining purified hydrogen from a gas mixtureby adsorption and regeneration by pressure modulation, called the PSAmethod, as described above, said method being characterized in that thegas mixture to be processed is a hydrogen-rich mixture furthercontaining CO₂ and CH₄, and in that said mixture passes successivelythrough two adsorbent beds, the first comprising activated charcoal andmicronodules of phase change material, the second comprising zeolite andmicronodules of phase change material, with paraffin being particularlypreferred.

The PSA method for the treatment of a gas mixture is further extremelyadvantageous for removing most of the water vapor present in the airwithout requiring heat treatment. Conventionally, such a method, called“air drying”, consists in passing the air to be dried over alumina orzeolite in a fixed bed in a column, and it is put into practiceadiabatically in the prior art. The heat of adsorption travels in thecolumn in the form of a faster front than the mass transfer front. Thetechnique employed consists in using a sufficiently long bed (between 1and 2 m) so that the heat front is maintained in the bed. Thus thecorresponding heat is available for the countercurrent purge gas whileminimizing the necessary quantity of purge gas. If the bed is too short,a portion of the heat of adsorption is lost and a larger quantity ofpurge gas is necessary. The cyclic operation of the method, combinedwith the need to maintain the thermal front in the bed, requireslimiting the penetration of the (slower) concentration front to arelatively short distance from the bed inlet. This penetration depthdepends on the moisture content, the cycle time and the adsorbent used.On the whole, the (oscillating) movement of the thermal front at the endof the bed presents a greater amplitude than that of the concentrationfront. Thus more than half of the bed downstream only operates asthermal ballast controlling the thermicity of the method by sensibleheat, which is less effective than control by latent heat. In the PSAmethod for drying air, the use of a composite material according to theinvention as adsorbent bed serves to ensure isothermal operation andconsequently to reduce the size of the bed, because the columncontaining the adsorbent material operates as adsorbent along its wholelength and under better conditions. The effective capacity of theinstallation is thereby improved. In consequence, a further subject ofthe present invention is a method for drying air by a PSA method asdescribed above, said method being characterized in that the gas mixtureto be processed is air containing water vapor, and in that the adsorbentbed is a composite material according to the invention in which theactive solid is an alumina or a zeolite, and the micronodules areparaffin micronodules.

Gas storage (natural gas, H₂ or CO₂ for example) can be carried out bycausing said gas to be adsorbed on an appropriate solid adsorbent (S.Biloé, V. Goetz, A. Guillot, Carbon, Vol. 40, pp. 1295-1308, 2002) underconditions such that the adsorption is reversible. This mechanism isexothermic in the adsorption direction and endothermic in the desorptiondirection. The generation of heat during the adsorption step, like theconsumption of heat during the desorption step, have detrimental effectson the yield of the operation (S. Biloé, V. Goetz, S. Mauran, AIChE J.,Vol. 47, pp. 2819-2830, 2001). The use of a composite material accordingto the invention as adsorbent solid serves to carry out the adsorptionstep under isothermal conditions, without using a device to remove theheat to the exterior, but by storing it in the form of latent heat ofphase change. This stored heat is then used to maintain a constanttemperature during the regeneration step, which is endothermic. This iswhy a further subject of the present invention is a method for storinggas by reversible adsorption on a porous solid, characterized in thatthe porous solid is a composite material according to the presentinvention, in which the active solid is a porous or a microporous solid.Zeolites and activated charcoal are particularly advantageous as activesolid in this method.

The production of oxygen by separating the components of air is achievedby cryogenic distillation, by a PSA method on zeolites 5A or 13X, or bya method called VSA (vacuum swing adsorption). The VSA method is similarto the PSA method described above, except as regards the regenerationstep, which is carried out under vacuum and not simply under reducedpressure with scavenging by a purge gas. In the PSA and VSA methods, theoxygen is fixed on the adsorbent. The VSA method is mainly controlled bythe sorption properties of the adsorbent, the influence of the masstransfer kinetics being substantially less [Budner Z., et al., Study andmodelling of the vacuum swing adsorption (VSA) process employed in theproduction of oxygen, Chemical Engineering Research and Design, Volume77, Issue 5, 1999, Pages 405-412]. Furthermore, during the applicationof a VSA method, it is important to reduce the effect of a cold pointdetrimental to the performance of the method. The steady stateconditions of the cyclic temperature profile of the process areestablished very slowly (about 1000 cycles or 12 to 15 hours), making itdifficult to optimize and hence to control the method [Wilson S. J., etal., Cyclic steady-state axial temperature profiles in multilayer, bulkgas PSA—The case of oxygen VSA, Industrial and Engineering ChemistryResearch, Volume 41, Issue 11, 29 May 2002, Pages 2753-2765]. Thetemperatures vary locally in sinusoidal mode with an amplitude of 5° C.and axially in the bed with an amplitude of 40° C., the uppertemperature being 290 K. It thereby appears that the optimization andcontrol of the method are considerably facilitated by isothermaloperation. Furthermore, since the method is controlled by the adsorptioncharacteristics of the adsorbent, isothermal operation at 290 K would bebeneficial for the effective capacity of the bed. The use of compositematerials according to the invention serves to obtain such isothermaloperation. A composite material comprising a bed of zeolite particles(5A, 13X ou CaX) and paraffin micronodules having a phase changetemperature close to 290 K (17° C.) is particularly appropriate. This iswhy a further subject of the present invention is a method forextracting oxygen from air by adsorption and regeneration by pressuremodulation, called the VSA method, consisting in carrying out thesuccessive steps of pressurization by air and placing an adsorbent bedunder vacuum, said method being characterized in that the adsorbent bedcomprises a composite material according to the invention, said materialpreferably comprising a zeolite and paraffin with a phase changetemperature close to 290 K. Hexadecane, pentadecane and heptadecane,which have melting points of 291.25 K, 283.05 K and 295.05 Krespectively, can be used advantageously as paraffin.

1. A composite material comprising an active solid and a phase changematerial, wherein: the phase change material takes the form ofmicronodules having an average size of between 1 micron and 5millimeters; the phase change material is selected from materials with aliquid/solid phase change temperature of between −150° C. and 900° C.;the active solid is selected from solids that can be used in a methodinvolving reversible physicochemical processes that are exothermic inone direction and endothermic in the opposite direction.
 2. Thecomposite material as claimed in claim 1, wherein the active solidcomprises a reactive solid that can be used in a reversible chemicalreaction.
 3. The composite material as claimed in claim 2, wherein thereactive solid is selected from halides, carbonates or hydroxides. 4.The composite material as claimed in claim 1, wherein the active solidcomprises a porous and/or microporous solid that can be used in areversible adsorption process.
 5. The composite material as claimed inclaim 4, wherein the porous and/or microporous active solid is selectedfrom activated charcoals, zeolites, activated alumina or silica gels. 6.The composite material as claimed in claim 1, wherein the phase changematerial is a paraffin or a mixture of paraffins.
 7. The compositematerial as claimed in claim 1, wherein the phase change material is acongruent melting salt.
 8. The composite material as claimed in claim 7,wherein the congruent melting salt is selected from hydrated orunhydrated halides, hydrated or unhydrated carbonates, hydrated orunhydrated sulfates, phosphates, nitrates or hydroxides.
 9. Thecomposite material as claimed in claim 8, wherein the congruent meltingsalt is selected from CaBr₂, CaCl₂, KF, KCl, MgCl, NaCl, NaF, NH₄Cl,NH₄F, ZnCl₂.5H₂O, KF.4H₂O, CaCl.6H₂O, LiClO₃.3H₂O, MgSO₄, ZnSO₄, Na₂SO₄,Na₂SO₄.10H₂O, (NH₄)₂SO₄, Na₂HPO₄, NaH₂PO₄, NH₄H₂PO₄, NH₄NC₃, Al(NO₃)₃,Ca(NO₃)₂, Cd(NO₃)₂, KNO₃, LiNO₃, Mg(NO₃)₂, NaNO₃, Ni(NO₃)₂, Zn(NO₃)₂,Zn(NO₃)₂.6H₂O, Cu(NO₃)₂, Ba(OH)₂ or NaOH.
 10. The composite material asclaimed in claim 1, wherein the phase change material is a metal. 11.The composite material as claimed in claim 10, wherein the metal isselected from Al, Pb, Cu, Zn and alloys thereof.
 12. The compositematerial as claimed in claim 1, wherein the active solid takes the formof particles or monoliths.
 13. The composite material as claimed inclaim 1, wherein it comprises a porous or microporous active solid, inthe form of monoliths or particles, the micronodules occupying the poresof the active solid.
 14. The composite material as claimed in claim 1,wherein it is formed by mixing particles or monoliths of active solidand micronodules, the micronodules occupying the spaces between theparticles or the monoliths of active solid.
 15. The composite materialas claimed in claim 1, wherein it comprises particles or monoliths ofactive solid on the surface of which the micronodules are fixed, eitherby chemical grafting or by bonding with an adhesive.
 16. The compositematerial as claimed in claim 1, wherein it comprises particles of activesolid fixed on the surface of the micronodules by chemical grafting orby bonding with an adhesive.
 17. The composite material as claimed inclaim 1, wherein it comprises a mixture of particles or monoliths ofactive solid, and particles of a support material on which themicronodules are fixed.
 18. The composite material as claimed in claim1, wherein it comprises one or a plurality of monoliths of active solidin which the micronodules are distributed.
 19. The composite material asclaimed in claim 1, wherein it further contains expanded naturalgraphite.
 20. A method for controlling thermal effects in a reversiblephysicochemical process between an active solid and a gaseous compound,said process being exothermic in one direction and endothermic in theopposite direction, wherein the thermal effects are controlled by usinga composite material as claimed in claim 1 as active solid.
 21. A methodfor purifying a gas mixture by adsorption and regeneration by pressuremodulation, called the PSA method, consisting in carrying out thesuccessive steps of pressurization and depressurization of at least oneadsorbent bed by a gas mixture, in order to separate the gas mixture,wherein the adsorbent bed(s) comprise(s) a composite material as claimedin claim
 1. 22. The method as claimed in claim 21, put into practice toobtain purified hydrogen from a gas mixture, wherein the gas mixture tobe processed is a hydrogen-rich mixture further containing CO₂ and CM₄,and in that said mixture passes successively through two adsorbent beds,the first comprising activated charcoal and micronodules of phase changematerial, the second comprising zeolite and micronodules of phase changematerial.
 23. The method as claimed in claim 21, put into practice todry air, wherein the gas mixture to be processed is air containing watervapor and in that the adsorbent bed is a composite material comprisingan alumina or a zeolite, and the micronodules are paraffin micronodules.24. A method for storing gas by reversible adsorption on a porous solid,wherein the porous solid is a composite material as claimed in claim 4.25. The method as claimed in claim 24, wherein the composite materialcomprises zeolite or activated charcoal.
 26. A method for extractingoxygen from air by adsorption and regeneration by pressure modulation,called the VSA method, consisting in carrying out successive steps ofpressurization by air and of placing an adsorbent bed under vacuum,wherein the adsorbent bed comprises a composite material as claimed inclaim
 1. 27. The method as claimed in claim 26, wherein said materialcomprises a zeolite and a paraffin with a phase change temperature closeto 290 K.